Abstract
The precise substrate specificities of an α-L-arabinofuranosidase from Trichoderma reesei were investigated. The enzyme released arabinose at appreciable rates from p-nitrophenyl-α-L-arabinofuranoside, O-α-L-arabinofuranosyl-(1→3)-O-β-D-xylopyranosyl-(1→4)-D-xylopyranose (A1X2), arabinan, arabinoxylan, arabinogalactan, debranched-arabinan and gum arabic, but not from O-β-D-xylopyranosyl-(1→4)-[O-α-L-arabinofuranosyl-(1→ 3)]-O-β-D-xylopyranosyl-(1→4)-D-xylopyranose (A1X3) or O-β-D-xylopyranosyl-(1→2)-O-α-L-arabinofuranosyl- (1→3)-O-β-D-xylopyranosyl-(1→4)-O-β-D-xylopyranosyl- (1→4)-D-xylopyranose (A1X4). The enzyme hydrolyzed methyl 2-O-, methyl 3-O- and methyl 5-O-α-L-arabinofuranosyl-α-L-arabinofuranosides to arabinose and methyl α-L-arabinofuranoside with the order of hydrolysis being: (1→5)->(1→2)-≥(1→3)-linkages. The enzyme hydrolyzed the (1→3)-linkage faster than the (1→5)- linkage of methyl 3,5-di-O-α-L-arabinofuranosyl-α-L-arabinofuranoside. The degree of conversion of arabinan and debranched-arabinan to monosaccharides by the enzyme was 33.0% and 9.1%, respectively. The α-L-arabinofuranosidase preferentially cleaved the arabinosyl sidechain from the arabinan rather than the terminal arabinosyl residue of the arabinan backbone.
